1. Field of the Invention
The present invention relates to circuits for the generation of step digital signals from binary signals of a very high bit rate.
2. Description of the Prior Art
The optimum use of the capacity of a transmission channel requires adaption of the signal to be transmitted to the signal/noise ratio in the transmission channel and to the band width of the channel. If a coaxial cable is employed as the transmission medium, then the path attenuation is approximately proportional to the square root of the signal frequency. Thus, with increasing transmission band width, the signal/noise ratio decreases quite quickly. The optimum exploitation of a digital signal is possible when the signal is transmitted not in binary form, but rather in the form of a signal with a plurality of amplitude steps, a socalled multi-step signal. As a rule, the number of steps selected for such signals is chosen so that the channel capacity becomes a maximum as the product of the resultant signal/noise ratio and the band width.
Circuits known in the art for the generation of such multi-step signals from binary inputs generally employ the technique of weighted addition, making use with very high bit rate inputs, in the range of at least a few hundred Mbit/s difficult.
Circuits known in the art employing the technique of weighted addition of binary signals encounter special difficulties with binary signal inputs in this range. At such a bit rate, exact weighting becomes difficult and the elimination of feedback so as not to affect the addition is also a problem. Circuits useable with lower bit rates can, therefore, not be readily adapted to use with bit rates in the hundred Mbit/s range.